1. Field of the Invention
The present invention relates to fibre channel systems, and more particularly, to a process and system for keeping an arbitrated loop open during frame gaps.
2. Background of the Invention
Fibre channel is a set of American National Standard Institute (ANSI) standards, which provide a serial transmission protocol for storage and network protocols such as HIPPI, SCSI, IP, ATM and others. Fibre channel provides an input/output interface to meet the requirements of both channel and network users.
Fibre channel supports three different topologies: point-to-point, arbitrated loop and fibre channel fabric. The point-to-point topology attaches two devices directly. The arbitrated loop topology attaches devices in a loop. The fibre channel fabric topology attaches host systems directly to a fabric, which are then connected to multiple devices. The fibre channel fabric topology allows several media types to be interconnected.
Fibre channel is a closed system that relies on multiple ports to exchange information on attributes and characteristics to determine if the ports can operate together. If the ports can work together, they define the criteria under which they communicate.
In fibre channel, a path is established between two nodes where the path's primary task is to transport data from one point to another at high speed with low latency, performing only simple error detection in hardware.
Fibre channel fabric devices include a node port or “N_Port” that manages fabric connections. The N_port establishes a connection to a fabric element (e.g., a switch) having a fabric port or F_port. Fabric elements include the intelligence to handle routing, error detection, recovery, and similar management functions.
A fibre channel switch is a multi-port device where each port manages a simple point-to-point connection between itself and its attached system. Each port can be attached to a server, peripheral, I/O subsystem, bridge, hub, router, or even another switch. A switch receives messages from one port and automatically routes it to another port. Multiple calls or data transfers happen concurrently through the multi-port fibre channel switch.
Fibre channel switches use memory buffers to hold frames received (at receive buffers) and sent across (via transmit buffers) a network. Associated with these buffers are credits, which are the number of frames that a buffer can hold per fabric port.
During an arbitrated loop mode, many cycles are wasted while arbitrating for the loop, or opening a device on the loop. If a sequence of frames had to go through arbitration and “OPEN” (as defined by the fibre channel standards), it could take more time arbitrating than keeping the loop open and waiting for the next frame of the sequence to arrive in the receive buffer.
Conventional switches do not stay open through frame gaps, and hence during the arbitrated loop mode when frames are coming from the same source in sequence, conventional switches are inefficient.
Therefore, there is a need for a process and system that can keep a loop open for a finite period of time during frame gaps so that entire sequence of frames can be delivered with only one OPEN.